Measurement of the details of the interactions of ionizing radiation with matter is a principal area of study in the fields of radiation physics, radiation protection and dosimetry. When ionizing radiation penetrates or passes through a gas and collides therewith, it produces electrons which in turn cause other ionizations and the production of additional electrons. Electrons are quickly thermalized. The system of the present invention measures the position of each of the thermal electrons produced and provides information concerning the three-dimensional spatial distribution of such electrons. Additionally, the system can be used in connection with the measurement of the quality of a laser beam and determining its three-dimensional profile. For example, when a laser beam penetrates a gas it produces ionizations, either by direct photon absorption or through resonance ionization, and the number of electrons produced in a given subvolume of the gas depends on the laser beam intensity therein. A measurement of the numbers of electrons produced in different subvolumes of a selected gas enables a determination of the three-dimensional beam profile.
Heretofore, devices commonly referred to in the literature as "streamer chambers" have been used to gather data concerning electron tracks produced in gases by ionizing radiation. Typically, streamer chambers apply a large DC pulse to enhance the production of ionized particles in the gas. The pulse is applied until image streamers, bright continuous tracks, are produced within the gas. However, streamer conditions produce space charge effects, i.e., the field generated by the electrons themselves approximates the order of magnitude of the applied electric field. Further, one is unable to gather data in a streamer chamber concerning the number of electrons produced in the electron track generated by the ionizing radiation.
When space charge effects are produced within the gas, the electric field becomes distorted, and the electron growth is non-linear. In such a situation, the representation of the electrons initially produced in the track is inaccurate. Moreover, in streamer chambers the presence of the track can be viewed, but the number of electrons therein cannot be determined. Streamer chambers also involve, in certain embodiments, complex chamber constructions together with complex electrode shapes and configurations. Moreover, sophisticated electronics are commonly required to determine the position of the electron tracks.
Accordingly, it is an object of the present invention to provide an ionizing radiation detector system capable of imaging the position of each electron produced in a particle track by ionizing radiation traveling through a gas and colliding therewith.
It is also an object of the present invention to provide means for determining the three-dimensional spatial position of each electron produced.
Another object of the invention is to provide a simpler system for imaging the position of each electron which avoids the need of drift chambers, or complex electrode shapes and configurations.
Yet another object of the present invention is to provide such a system which can be used in connection with the analysis of the electromagnetic spectrum from visible through gamma-ray radiation.